This invention is related to III-Nitride based light-emitting diodes (LEDs). Over the past decade, group III-nitride based light-emitting devices have garnered significant attention due to the ability of group III-nitride based devices to output light having wavelengths in the ultra-violet (UV), blue and green light regimes. Despite the significant resources expended to develop and commercialize group III-nitride based light-emitting devices significant difficulties and barriers still exist to realizing group III-nitride based light-emitting devices with improved efficiency, reliability and performance characteristics. Conventional standard III-Nitride LEDs require that electrons are injected into the semiconducting device such that the electron potentials are at the conduction-band minimum of the n-type layer, for the purpose of later being injected into a lower-potential active region. The potential level of the initial electron injection determines the voltage that is required to drive the LED. Once the electrons are initially injected into the conventional standard LED device, the electrons drop in energy into an energy potential of the sub-band minimum of the active region from the n-type semiconductor conduction-band minimum and then combine with a positive carrier, thereby releasing energy as a photon. The initial drop in energy of the electron from the bottom of the n-type conduction band to the energy potential of the sub-band minimum of the active region is converted into heat and therefore wasted energy. This wasted energy is an issue because the generation of heat is not desirable due to decreased device reliability, and LEDs that are efficient in converting electrical energy to light are favored. Moreover, in conventional LEDs, the electrons may travel past the quantum wells into the p-type materials, where the electrons are recombine with holes outside of the active region of the device and therefore the energy expended to move the electrons into the conduction band of the n-GaN is wasted. One example of a conventional LED device that exhibits the prior mentioned limitation is shown in prior-art FIGS. 1A, 1B, and 1C.
U.S. Pat. No. 6,614,060 issued to Wang et al. on Sep. 2, 2003 titled “LIGHT EMITTING DIODES WITH ASYMMETRIC RESONANCE TUNNELING”, and is incorporated herein by reference in its entirety for all purposes. Wang et al. describe an LED based on a two well system with charge asymmetric resonance tunneling that comprises first and second coupled wells, one being a wide well and the other an active quantum well. The wells are coupled via a resonance tunneling barrier which is substantially transparent for quantum-tunneling electrons and blocking for holes.
U.S. Pat. No. 6,426,512 to Ito et al. titled “GROUP III NITRIDE COMPOUND SEMICONDUCTOR DEVICE”, and is incorporated herein by reference in its entirety for all purposes. Ito et al. describe an undercoat layer inclusive of a metal nitride layer that are formed on a substrate. Group III nitride compound semiconductor layers are formed on the undercoat layer continuously.
U.S. Pat. No. 7,176,483 to Grupp et al. titled “METHOD FOR DEPINNING THE FERMI LEVEL OF A SEMICONDUCTOR AT AN ELECTRICAL JUNCTION AND DEVICES INCORPORATING SUCH JUNCTIONS”, and is incorporated herein by reference in its entirety for all purposes. Grupp et al. describe an electrical junction that includes a semiconductor (e.g., C, Ge, or a Si-based semiconductor), a conductor, and an interface layer disposed therebetween. The interface layer is sufficiently thick to depin a Fermi level of the semiconductor, yet sufficiently thin to provide the junction with a specific contact resistance of less than or equal to approximately 1000 Ω-μm2, and in some cases a minimum specific contact resistance.
There is a need for improved light-emitting diodes, particularly group III-nitride LEDs, and in particular, group III-nitride LEDs that use resonant tunneling barriers.